The damage caused by the Auckland floods and Cyclone Gabrielle has put homeowners with basements on notice.
Many articles that appeared in the immediate aftermath of the weather events have referred to flooded basements and below ground garages. And data analysis suggests some of these affected basements will have been recently consented.
According to research by OneRoof’s data partner Valocity, 296 consents for basements have been issued in Auckland since 2010. “Most of these won’t be actual American-style a hole in the ground basement,” James Wilson, head of valuations at Valocity, said. “They will be space added under the home for living or garaging.”
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Environmental engineer Aidan Cooper told OneRoof garages and basements had not been designed for the intensity of rainfall that New Zealand had experienced in the past few weeks. “It was so much larger than anything we have designed for in the past. Some recently consented properties have been affected.”
Auckland suffered at the end of January a 100-year flood – a flood event that has a one in 100 chance of being exceeded in any given year – but Cooper said stormwater pipes in newer areas were designed for a 10-year flood event, and in some older areas can only cope with a five-year flood.
In a press conference following January’s extreme downpour, Auckland Council’s head of planning for healthy waters, Nick Vigar, warned residents not to use basements as living spaces – or even carpet them.
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He also urged homeowners with basement spaces to add resilient internal linings and raise any power points, although he added that most developments built in the past decade in the city should be reasonably resilient to the flooding.
Owners in older areas may not be so lucky. “Tools have only matured over the past couple of decades,” Vigar said at the press conference. “That wasn’t available when most of Auckland developed over the past 125 years. Once you have overwhelmed your pipe network it is naturally going to flow to those points that we refer to as overland flow paths.”
Although it will be cold comfort to some homeowners, the positive for many is that they now know what they’re dealing with and can plan accordingly, Cooper told OneRoof.
“If a property, garage, or basement is at risk of flooding, people have a warning now and they can take precautions as a landowner to protect their assets.”
In the UK, where Cooper worked previously, flood risks are added to property titles, and an early warning system gives residents 24 hours’ notice of an impending flood. “In that 24 hours you will put floodgates in and move the car up the hill,” he said.
“I’m not expecting that to happen now in New Zealand, but it is a positive that we have that awareness. If we see a large event bearing down, people can take steps to protect their properties.”
Cooper said engineers were learning from events such as the ones New Zealand has just experienced and the technology is improving. However, some homeowners may choose to turn basements used for habitation currently back into garages. “It comes down to the level of risk that the individual or the homeowner is looking for.”
- Cyclone Gabrielle: Click here to donate to the New Zealand disaster fund
